The present invention relates to a method for increasing the bearing capacity of foundation soils for built structures, including buildings, roadway slabs, airport runaways and equipment supporting slabs.
Any building requires the foundation soil to have a sufficient bearing capacity to support it. Otherwise, the settling of the foundation soil leads to the failure of the overlying building, regardless of whether the settling occurs in the uppermost or in the deep layers.
Before erecting any building, the bearing capacity of the soil is therefore estimated according to the weight or load which the building will apply to the soil, even using, if necessary, appropriate soil research, such as for example geological and geotechnical research.
In order to ensure the stability of the structure, the optimum dimensions of the foundations and their rigidity are calculated and the depth of the foundations is also determined, adequately balancing their weight in relation to the bearing capacity of the soil and always maintaining a good safety margin. In case of error, the building may in fact fail.
Often, however, the bearing capacity of the foundation soil is not sufficient, since the soil is compressible, as in the case of filled-in land, non-consolidated land, land with decomposing organic layers, peaty land, swampy land, land with considerable variations in water content, flooded or washed-out land with voids or with non-uniform or insufficiently aggregated masses, land with interstitial voids, et cetera; or the building is very heavy and requires a greater bearing capacity than the actual bearing capacity of the foundation soil.
Various conventional systems ensure in any case the stability of the building. Generally, these systems tend to directly transfer the weight of the building to the deeper and adequately solid soil layers or to spread the load over a wide ground surface, such as for example the method consisting in driving piles or micropiles and the like into the foundation soil. This method can be used both before and after construction.
Of course, the driving of piles and micropiles or the like after the construction of the building is extremely complicated and expensive.
Conventional methods also cope with any subsidence of the building after its construction, such as for example the method described in U.S. Pat. No. 4,567,708, which entails the injection of an expandable substance beneath the building to fill the interstices which have formed and have caused the subsidence and in order to recover the subsidence of the building, or other lifting methods.
In the method disclosed in the above-cited patent, as well as in other lifting systems, however, the foundation soil is not treated; at the most, one acts on the surface layers of the soil, and therefore if the underlying soil has not settled enough, further subsequent subsidence of said building will occur over time.
A method for ground consolidation using, an expandable substance, in which the expansion time is controlled to be slow or very slow, is known from the document DE-A-33 32 256.
A principal aim of the present invention is to solve the above problems by providing a method capable of ensuring the stability of built structures, including buildings, roadway slabs, airport runaways and equipment supporting slabs, by adequately treating the foundation soil in order to increase its bearing capacity. The term xe2x80x9cfoundation soilxe2x80x9d is intended to designate that part of the soil having influence on the overlying built structure or that the direct or indirect influence of the built structure (J. Collas and M Harvard, Manuale di Geotecnica, Faenza Editrice S. P. A., 1986).
Within the scope of this aim, an object of the present invention is to provide a method which does not require the use of cement, concrete, or metal structures driven into the ground, such as piles, micropiles, cement injections, very deep foundations, etcetera.
Another object of the present invention is to provide a method which is simple and easy to perform and can be adopted to increase the bearing capacity of foundation soils both before and after construction of the building.
This aim, these objects, and others which will become apparent hereinafter are achieved by a method for increasing the bearing capacity of foundation soils for built structures, according to the present invention, comprising the steps set forth in claims.